feat: add option to send legacy style x-amx-user-agent header to s3 server

[icewind1991]

• Resolves: #

Summary

Starting with aws-sdk 3.336.0, the user agent headers sent by the sdk have changed.

Previously, the X-Amz-User-Agent and User-Agent header would both contain the same user agent.

Since 3.336.0, the X-Amz-User-Agent no longer contains the user agent but is sent empty instead.

This seems to break some s3 implementations, so we can add a middleware to re-add the value

TODO:

• Verify that this fixes the issue with the problematic s3 implementation
• Document the config flag

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI